WASHINGTON — President Barack Obama's pledge of bipartisan cooperation with Congress will be tested as he tries to fulfill a campaign promise to close Guantanamo Bay and establish a new system for prosecuting suspected terrorists.

The undertaking is an ambitious one. Fraught with legal complexities, it gives Republicans ample opportunity to score political points if he doesn't get it right. There's also the liklihood of a run-in with his former rival, Sen. John McCain, a former prisoner of war who before running for president staked his career on overhauling the nation's detainee policies.

"We look forward to working with the president and his administration on these issues, keeping in mind that the first priority of the U.S. government is to guarantee the security of the American people," McCain, R-Ariz., said in a joint statement with Sen. Lindsey Graham, R-S.C.

The statement seemed aimed at putting Obama on notice that he must deal with Congress on the matter.

In his first week in office, Obama ordered Guantanamo Bay prison in Cuba to be closed within a year, CIA secret prisons shuttered and abusive interrogations ended.

So far, Obama's team has given every indication it will engage lawmakers, including Republicans, on the issue. Graham and McCain were among several Republicans briefed last week by White House counsel Greg Craig and handed drafts of the executive orders.

Ample room for dispute
But once the two sides begin delving into details, there will be ample room for dispute.

Among the unknowns is how many of the 245 detainees now at Guantanamo Bay will be prosecuted.

Administration officials said that, pending an internal review, federal and military courts may be used. But, the officials added, a version of the secretive military tribunals, as established under President George W. Bush with the help of McCain, remains an option, too.

Officials say the tribunals may be needed to prosecute suspected terrorists who are too dangerous to release but whose cases would otherwise fail, either because evidence was coerced or trying them in a less secretive court would expose classified information.

Obama could take a page from the Bush administration and try to revamp the system on his own, through executive order. But that approach failed for Bush, who angered members of his own party and wound up seeking congressional approval anyway after the Supreme Court in June 2006 ruled his tribunal system was unconstitutional.

Obama's other option is to seek legislation on the issue, potentially exposing his administration to a bruising fight with Republicans on how to handle the most dangerous of terrorism suspects.

A narrow majority of Americans supports shutting down Guantanamo Bay on a priority basis. But people are likely to become much less sympathetic to detainee rights if there is another terrorism attack inside the United States or if the new system is portrayed as too lenient on suspected al-Qaida members.

Soft on terrorism?Republicans already are trying to portray Obama's review of detainee rights as soft on terrorism. House Republicans on Friday mobilized a "rapid response team" of lawmakers to speak out against the president's plans.

"The Guantanamo Bay prison is filled with the worst of the worst — terrorists and killers bent on murdering Americans and other friends of freedom around the world," said House GOP leader John Boehner of Ohio. "If it is closed, where will they go, will they be brought to the United States and how will they be secured?"

Democrats have suggested they expect to be important players in the debate.

Sen. Dianne Feinstein, D-Calif., who heads the Senate Select Committee on Intelligence, said the panel planned to hold back on legislation "for a time" to allow the administration to complete its own assessment. Sen. Carl Levin, D-Mich., chairman of the Senate Armed Services Committee, said he would like "to at least have an advisory role" on the final plan.

In 2006, the question of detainee trials and interrogations enveloped Congress and exposed Republican infighting. McCain, Graham and now retired Sen. John Warner, R-Va., sharply challenged Bush's handling of detainees. In the end, the two sides emerged with complex legislation that outlined the inner workings of military tribunals and defined what constitutes a war crime, effectively banning specific interrogation techniques seen as too harsh.

'We are at war'Human rights groups and Democrats said the system still gave too much power to the president. But now, Republicans are worried Obama will swing too far in the other direction.

Graham, a colonel in the Air Force Reserves assigned to the service's Judge Advocate General School, said he is concerned that Obama will wind up giving civilian courts too heavy a hand in dealing with terrorists handled by the military and CIA.

"Federal judges in my opinion should not be making battlefield decisions. ... I don't want to lose sight of the fact that we are at war," he said.

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